Binary Stacks Research Articles

Fiji-Assisted Automatic Quantitative Volumetric Analysis of Choroidal Neovascularization in a Laser-Induced Choroidal Neovascularization Mouse Model.

The laser-induced choroidal neovascularization (CNV) mouse model is the most frequently used animal model of CNV. To test new therapeutic agents that suppress CNV, CNV measurement in an accurate, precise, and efficient manner is important. We present the utility of Fiji-assisted automatic volumetric quantification of CNV in comparison with two-dimensional CNV analyses. Laser-induced CNV was induced in C57BL/6J mice according to the established protocol. After CNV induction, mice were treated with intravitreal injection of either phosphate-buffered saline solution (PBS) or Aflibercept, an anti- vascular endothelial growth factor agent. One week after intravitreal injection treatment, retina pigment epithelium/choroid flat mounts were stained with rhodamine-conjugated Griffonia simplicifolia lectin B4. Z-stacks of the entire CNV lesion obtained using laser confocal microscopy were converted to binary stacks using Fiji for volumetric analysis. Data from volumetric analysis and multiple area analyses from z-stack projection, the maximum, blindly selected, and mean area were compared using Fiji. Fiji-assisted automatic quantitative volumetric analysis of CNV was useful in detecting experimental outliers in laser-induced CNV genesis and provided accurate and precise measurements of total areas of CNV with a lower coefficient of variance (63%) than in multiple area analyses, including the z-stack projection, maximum, blindly selected, and mean areas (67%, 67%, 76%, and 69%, respectively). A lower coefficient of variance in volumetric analysis than in multiple area analyses resulted in increased statistical significance when comparing CNV lesions in PBS, and Aflibercept-treated groups; P = 0.004 in volumetric analysis versus P value range between 0.03 and 0.05 in multiple area analyses. Fiji-assisted automatic quantitative volumetric analysis can be useful for accurate, precise, and efficient measurements of total areas of CNV. Volumetric measurement for CNV lesions can be advantageous in verifying the efficacy of therapeutic agents in the laser-induced CNV mouse model.

Theoretical evaluation of emerging Cd-free Cu3BiS3 based solar cells using experimental data of chemically deposited Cu3BiS3 thin films

The present research involves a combined experimental and theoretical study to evaluate the optoelectronic properties of Cu3BiS3 (CBS) semiconductor as an effective solar absorber in thin film photovoltaics. Our study consists of the synthesis and characterization of CBS films, followed by the execution of performance analysis as absorber material in a single heterojunction solar cell using numerical simulation by loading the individual material parameters for each layer of CBS solar cell into SCAPS-1D software. In the case of CBS layer, we considered the physical properties of CBS obtained experimentally in this work. The active layer was obtained by thermal diffusion of chemically deposited Bi2S3/CuS binary stacks at 300 °C and 350 °C in an inert atmosphere. Energy-dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy studies confirm the appropriate composition as well as the formation of well-crystalline and single-phase orthorhombic Cu3BiS3 structure. Promising electrical properties were revealed by Hall effect measurements. The performance of the CBS layer was investigated considering the traditional CdS buffer layer and a Cd-free buffer layer such as Bi2S3. The higher conversion efficiency of 7.6% was obtained for CBS/Bi2S3 heterostructure compared with 6.8% efficiency using CdS buffer. A suitable band alignment at the CBS/Bi2S3 interface and ohmic back contact at Mo/CBS junction resulted to be mainly responsible for the enhanced efficiency.

Effective Property Uncertainty of Graphite Electrodes from Computed Tomography Using Bayesian Convolutional Neural Networks

In recent years there have been great advances in using 3D tomography in battery research, providing the ability to see as-manufactured electrodes at the mesoscale. These structures are subsequently used to find effective properties or perform detailed electrochemical simulations. A key step of this analysis is image segmentation, which differentiates particle and void phases. Image segmentation, however, is painstaking and fraught with subjectiveness. Removing this subjectiveness is paramount in having credible direct numerical simulations to bridge the gap of the computational and experimental regimes. To improve the image segmentation process and quantify its uncertainty, a Bayesian convolutional neural network (BCNN) is implemented to segment greyscale tomograms of graphite electrodes. The use of a BCNN allows for native and explainable uncertainty estimates. Two manually segmented tomograms were used to train the BCNN, which was in turn used to segment an additional four tomograms. This process was effective in creating high quality binary stacks, which in some cases presented a subjectively superior segmentation compared to the manual process. Additionally, BCNN-generated uncertainty estimates provide a range of possible image segmentations and structures. These nominal and uncertainty ranged structures are propagated through simulations of effective electrical conductivity and pore phase tortuosity, providing both nominal property predictions and geometric uncertainty estimates of those predictions. This work demonstrates a new method for quantifying geometric uncertainty from as-manufactured electrode images and the impact of that uncertainty regarding battery-relevant physical phenomena.

Coordination Chemistry of Anticrowns. Synthesis and Structures of Complexes of the Perfluorinated Three‐Mercury Anticrown (o‐C6F4Hg)3 with Monohalogenobenzenes

The paper reports the reactions of the perfluorinated three‐mercury anticrown (o‐C6F4Hg)3 (1) with monohalogenobenzenes. It has been found that the interaction of 1 with fluorobenzene gives two 1:1 complexes 2 and 3, differing in their structures. Complex 2 forms in the crystal extended binary stacks wherein the molecules of 1 alternate with the halogenobenzene species, while complex 3 consists of the cofacial dimers formed from the corresponding monomeric units {[(o‐C6F4Hg)3](C6H5F)}. Each fluorobenzene molecule in both adducts is bonded to 1 by its phenyl ring through secondary π‐Hg–C interactions, whereas the fluorine atom is coordinated with one of the Hg sites of 1. Analogous types of bonding are realized in the chlorobenzene and bromobenzene complexes, {[(o‐C6F4Hg)3]2(C6H5X)4}, (X = Cl, Br), containing four halogenobenzene molecules per two molecules of 1. The complexes include two monomeric {[(o‐C6F4Hg)3](C6H5X)2} fragments connected with one another by two bridging η1 coordinated halogen atoms of the halogenobenzene ligands. The halogen atoms of two other halogenobenzene species are η3 coordinated each with the Hg centers of the neighboring molecule of 1. The reaction of iodobenzene with 1 affords a 3:1 complex, {[(o‐C6F4Hg)3](C6H5I)3}, which is unstable and readily transformed into the corresponding 1:1 adduct. Both compounds form in the crystal extended stacks wherein each sandwiched iodobenzene molecule is coordinated via the iodine atom with the adjacent molecule(s) of 1.

Testing species assemblage predictions from stacked and joint species distribution models

AbstractAimPredicting the spatial distribution of species assemblages remains an important challenge in biogeography. Recently, it has been proposed to extend correlative species distribution models (SDMs) by taking into account (a) covariance between species occurrences in so‐called joint species distribution models (JSDMs) and (b) ecological assembly rules within the SESAM (spatially explicit species assemblage modelling) framework. Yet, little guidance exists on how these approaches could be combined. We, thus, aim to compare the accuracy of assemblage predictions derived from stacked and from joint SDMs.LocationSwitzerland.TaxonBirds, tree species.MethodsBased on two monitoring schemes (national forest inventory and Swiss breeding bird atlas), we built SDMs and JSDMs for tree species (at 100 m resolution) and forest birds (at 1 km resolution). We tested accuracy of species assemblage and richness predictions on holdout data using different stacking procedures and ecological assembly rules.ResultsDespite minor differences, results were consistent between birds and tree species. Cross‐validated species‐level model performance was generally higher in SDMs than JSDMs. Differences in species richness and assemblage predictions were larger between stacking procedures and ecological assembly rules than between stacked SDMs and JSDMs. On average, predictions were slightly better for stacked SDMs compared to JSDMs, probabilistic stacks outperformed binary stacks, and ecological assembly rules yielded best predictions.Main conclusionsWhen predicting the composition of species assemblages, the choice of stacking procedure and ecological assembly rule seems more decisive than differences in underlying model type (SDM vs. JSDM). JSDMs do not seem to improve community predictions compared to SDMs or improve predictions for rare species. Still, JSDMs may provide additional insights into community assembly and may help deriving hypotheses about prevailing biotic interactions in the system. We provide simple rules of thumb for choosing appropriate modelling pathways. Future studies should test these preliminary guidelines for other taxa and biogeographical realms as well as for other JSDM algorithms.

Optonumerical technique for mapping freezing droplet interactions on substrates

A visualization technique was developed to accurately resolve the locations and phases of liquid and frozen water droplets naturally evolving on a subfreezing surface exposed to a humid air stream. The technique utilized the lens-like properties of unfrozen condensate droplets to focus reflected light in a manner that made it possible to reliably distinguish the unfrozen from frozen droplets. By inducing this lensing effect in all visible droplets on the surface prior to freezing, a small, high contrast region within each liquid droplet was produced. When freezing occurred, the higher opacity of the ice phase caused the frozen droplets to suddenly take on a darker appearance than the unfrozen droplets. A reflected light microscope and digital camera apparatus were used to feed data into an image analysis algorithm capable of mapping the time-evolution of the freezing water droplets on the surface. The algorithm processed raw image sequences into binary image stacks from which the light foci associated with the droplets could be reliably isolated into high contrast white pixel clusters on an otherwise black background. An edge detection method was employed within each binary image to locate the coordinates of the pixels residing along the periphery of each droplet’s focal cone. Those data were subsequently used to compute the centroidal coordinates and state of each droplet over time. Compared with more laborious, frame-by-frame analyses with various commercially available software tools, this technique correctly identified the locations and states of the droplets through the entire growth and freezing processes with accuracies in excess of 99%. This technical approach also allowed for simultaneous tracking of all droplets and freezing events present within the region of interest—typically numbering in the hundreds or thousands—over time, paving the way for interdroplet coalescence and freezing interactions to be studied in detail.

Face-to-Face Stacks of Trinuclear Gold(I) Trihalides with Benzene, Hexafluorobenzene, and Borazine: Impact of Aromaticity on Stacking Interactions

The interplay of electrostatics, charge transfer, and dispersion forces contributing to the interaction energies in 1:1, 1:2, and 2:1 binary stacks of the c-Au(3)(μ(2)-X)(3) (X = F, Cl, Br, I) clusters with benzene, hexafluorobenzene, or borazine were investigated by employing a multitude of electronic structure computational techniques. The molecular and electronic structures, stabilities, bonding features, and magnetotropicity of [c-Au(3)(μ(2)-X)(3)](n)(L)(m) (X = halide; L = C(6)H(6), C(6)F(6), B(3)N(3)H(6); n, m ≤ 2) columnar binary stacks have been investigated by DFT calculations employing the M05-2X functional. The novel binary stacks could be considered as the building blocks of extended columnar supramolecular assemblies formulated as {[c-Au(3)(μ(2)-X)(3)](C(6)H(6))}(∞), {[c-Au(3)(μ(2)-X)(3)](2)(C(6)F(6))}(∞), and {[c-Au(3)(μ(2)-X)(3)](B(3)N(3)H(6))(2)}(∞). In all binary stacks, with a few exceptions, the plane of the alternating c-Au(3)(μ(2)-X)(3) and L (C(6)H(6), C(6)F(6), B(3)N(3)H(6)) stacking participants adopt an almost parallel face-to-face (pff) orientation. The observed trends in the intermolecular distances R in the [c-Au(3)(μ(2)-X)(3)](n)(L)(m) (X = halide; L = C(6)H(6), C(6)F(6), B(3)N(3)H(6); n, m ≤ 2) columnar binary stacks are explained by the diverse intermolecular interactions characterizing the stacks, since the three ligands L and the c-Au(3)(μ(2)-X)(3) cyclic trinuclear clusters (CTCs) exhibit diverse physical properties being important determinants of the intermolecular interactions (consisting of covalent, electrostatic, and dispersion forces). The properties considered are the zz tensor components of quadrupole moment, Q(zz), polarizability, α(zz), nucleus-independent chemical shift, NICS(zz)(1), along with the molecular electrostatic potential, MEP(0), and surface area (S). Energy decomposition analysis (EDA) at the revPBE-D3/TZ2P level revealed that the dominant term in the stacking interactions arises mainly from dispersion and electrostatic forces, while the contribution of covalent interactions are predicted to be small. On the other hand, charge decomposition analysis (CDA) illustrated very small charge transfer from the L stacking participants toward the c-Au(3)(μ(2)-X)(3) clusters. Excellent linear correlations of the interaction energy, ΔE(int), and its components (ΔE(disp), ΔE(elstat), ΔE(orb), and ΔE(Pauli)) with calculated physical properties related to dispersion, covalent, and electrostatic forces have been established. The most important finding is the excellent linear relationship between ΔE(int) and the NICS(zz)(1) magnetic criterion of aromaticity, indicating that ΔE(int) is also affected by the coupling of the induced magnetic fields of the interacting stacking participants. The magnetotropicity of the binary stacks evaluated by the NICS(zz)-scan curves indicated an enhancement of the diatropicity in the space between the interacting inorganic and organic rings, probably due to the superposition of the diamagnetic ring currents of the interacting ring systems. The energy splitting in dimer (ESID) model was employed to estimate the charge transport of electrons and holes between the ligands L and the [c-Au(3)(μ(2)-X)(3)] clusters in [c-Au(3)(μ(2)-X)(3)](L) 1:1 binary stacks.

Molecular and Electronic Structure, Magnetotropicity and Absorption Spectra of Benzene–Trinuclear Copper(I) and Silver(I) Trihalide Columnar Binary Stacks

The molecular and electronic structures, stabilities, bonding features, magnetotropicity and absorption spectra of benzene-trinuclear Cu(I) and Ag(I) trihalide columnar binary stacks with the general formula [c-M(3)(μ(2)-X)(3)](n)(C(6)H(6))(m) (M = Cu, Ag; X = halide; n, m ≤ 2) have been investigated by means of electronic structure calculation methods. The interaction of c-M(3)(μ(2)-X)(3) clusters with one and two benzene molecules yields 1:1 and 1:2 binary stacks, while benzene sandwiched 2:1 stacks are formed upon interaction of two c-M(3)(μ(2)-X)(3) clusters with one benzene molecule. In all binary stacks the plane of the alternating c-M(3)(μ(2)-X)(3) and benzene components adopts an almost parallel orientation. The separation distance between the centroids of the benzene and the proximal c-M(3)(μ(2)-X)(3) metallic cluster found in the range 2.97-3.33 Å at the B97D/Def2-TZVP level is indicative of a π···π stacking interaction mode, for the centroid separation distance is very close to the sum of the van der Waals radii of Cu···C (3.10 Å) and Ag···C (3.44 Å). Energy decomposition analysis (EDA) at the SSB-D/TZP level revealed that the dominant term in the c-M(3)(μ(2)-X)(3)···C(6)H(6) interaction arises from dispersion and electrostatic forces while the covalent interactions are predicted to be negligible. On the other hand, charge decomposition analysis (CDA) illustrated very small charge transfer from C(6)H(6) toward the c-M(3)(μ(2)-X)(3) clusters, thus reflecting weak π-base/π-acid interactions which are further corroborated by the respective electrostatic potentials and the fact that the total dipole moment vector points to the center of the metallic ring of the c-M(3)(μ(2)-X)(3) cluster. The absorption spectra of all aromatic columnar binary stacks simulated by means of TD-DFT calculations showed strong absorptions in the UV region. The main features of the simulated absorption spectra are thoroughly analyzed, and assignments of the contributing electronic transitions are given. The magnetotropicity of the binary stacks evaluated by the NICS(zz)-scan curves indicated an enhancement of the diatropicity of the inorganic ring upon interaction with the aromatic benzene molecule. Noteworthy is the slight enhancement of the diatropicity of the benzene ring, particularly in the region between the interacting rings, probably due to the superposition (coupling) of the diamagnetic ring currents of the interacting aromatic ring systems.

Probing the stacking properties of nucleosides and nucleotides with heteroaromatic amines and the effect of metal ion-bridging on the stability of the stacks. Implications for biological systems

Noncovalent interactions play important roles in modern chem. research encompassing also bio- systems. Among these interactions arom.-ring stacking is esp. pronounced as, next to hydrogen bonding, hydrophobic and ionic interactions, it is crucial for the three-dimensional structure of nucleic acids (RNA, DNA) and proteins (enzymes). The authors have now measured by 1H-NMR shift expts. the stability of binary stacks formed between purine nucleosides or nucleotides (N) and the indicator ligand 1,10-phenanthroline (Phen), and the authors also reviewed the related literature. Surprisingly, the stability of the (Phen)(N) adducts is largely independent of the type of purine residue involved, including deprotonation, e.g., at (N1)H of a guanine moiety, and also of the location of the phosphate group at the ribosyl ring. This contrasts with the self-stacking tendency which decreases within the series adenosine < guanosine < inosine < cytidine approx. uridine. The formation of an ionic (+/-) or metal ion (M2+) bridge stabilizes the formation of stacks as obsd., e.g., in mixed ligand Cu2+ complexes formed between Phen and AMP (5'-AMP2-); yet, in these instances the position of the phosphate group at the ribosyl ring affects the stability of the stacks: It decreases in the order 2'-AMP2- < 5'-AMP2- < 3'-AMP2- in the Cu(Phen)(AMP) complexes demonstrating a significant steric discrimination. The stability of stacks also depends on the size of the arom.-ring systems involved; as one would expect, purines stack better than pyrimidines and Phen generally better than 2,2'-bipyridine. Results obtained with various mixed ligand metal ion complexes contg. ATP (ATP4-) and an amino acid anion (Aa-) lead to the conclusion: The recognition of the adenine residue by the amino acid side chain in M(ATP)(Aa)3- complexes decreases in the series tryptophan (indole residue) < histidine (imidazole residue) < leucine (iso-Pr residue) < alanine (Me group). This type selectivity is certainly of relevance for amino acid/protein interactions with nucleotides/nucleic acids. The addn. of an org. solvent like 1,4-dioxane reduces the solvent polarity and decreases the stability of binary stacks like (Phen)(ATP)4- dramatically; in contrast, intramol. stacks, as present in Cu(Phen)(ATP)2-, are much less affected. Because the effective dielec. const. or permittivity in the active site cavity of an enzyme or a ribozyme is lower than in bulk water, Nature has here a further tool to achieve selectivity. Here it needs to be noted that the involved changes in free energy (ΔG0) are small; e.g., a formation degree of 20% of an intramol. stack in a mixed ligand complex corresponds only to -0.6 kJ mol-1 allowing Nature to shift such equil. easily.

Binary stacks of [CuC6F5]4 with arenes

Formation of the first binary stacks of an intact organocopper aggregate with the arenes naphthalene and 2,2'-bithiophene is reported; crystallographic data suggest that the supramolecular assembly process is supported by Cu-pi, Cu-S, and perfluoroarene-arene pi-interactions.

Synthesis, structures, and luminescence properties of ternary supramolecular hydrogen‐bonded complexes involving [(o‐C6F4)Hg]3, carbazole, and a Lewis base

AbstractThe interaction of trimeric perfluoro‐ortho‐phenylene mercury (1) with carbazole in dichloromethane, THF, and THF/NEt3 leads to the crystallization of [1·C12H8NH] (2), [1·(C12H8NH·THF)] (3), and [1·(C12H8NH·NEt3)] (4), respectively. Adducts 3 and 4 have been characterized by elemental analysis, IR spectroscopy, and luminescence spectroscopy. The crystal structures of 3 and 4 have also been determined. Both adducts have extended structures that exhibit supramolecular binary stacks, where molecules of 1 and the carbazole–Lewis base complex alternate. Short Hg–C contacts involving molecules of 1 and carbazole indicate the presence of secondary Hg–π interactions. In addition, adducts 3 and 4 display hydrogen‐bonding interactions between the acidic NH moiety of carbazole and the heteroatom of the Lewis base. The presence of this hydrogen bond is also confirmed by IR spectroscopy, which shows that the νNH of 3 and 4 is lower than that of 2. The luminescence spectra of these adducts correspond to the phosphorescence of carbazole, which is induced by the mercury heavy atom effect. In the case of 3 and 4, additional low‐energy bands are observed at 578 and 567 nm. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:195–201, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20329

Enhancement of External Spin−Orbit Coupling Effects Caused by Metal−Metal Cooperativity

As part of our efforts to discover simple routes to room-temperature phosphors, we have investigated the interaction of bis(pentafluorophenyl)mercury (1) or trimeric perfluoro-o-phenylene mercury (2) with selected arenes (naphthalene, biphenyl, and fluorene). Solution studies indicate that 2, unlike 1, quenches the fluorescence of naphthalene. When compared to 1, the high quenching efficiency of 2 may be correlated to the higher affinity that 2 displays for arenes as well as to more acute external heavy-atom effects caused by the three mercury atoms. In the crystal, the adducts [1.naphthalene], [1.biphenyl], [1.fluorene], and [2.fluorene] form supramolecular binary stacks in which the arene approaches the mercury centers of 1 or 2 to form Hg-C pi-interactions. Analysis of the electrostatic potential surfaces of the individual components supports the involvement of electrostatic interactions. The luminescence spectra of the adducts show complete quenching of the fluorescence and display heavy-atom-induced emission whose energies and vibronic progressions correspond to the phosphorescence of the respective pure arene. The phosphorescence lifetimes are shortened by 3 or 4 orders of magnitude when compared with those of the free arenes. Taken collectively, the structural, photophysical, and computational results herein suggest that the proximity of the three mercury centers serves to enhance the Lewis acidity of 2, which becomes a better acceptor and a more effective heavy-atom effect inducer than 1.

Structural and photophysical studies of phenanthrene adducts involving C6F5HgCl and [o-C6F4Hg

Both pentafluorophenylmercury chloride and trimeric perfluoro-ortho-phenylene mercury interact with phenanthrene to form phosphorescent adducts which exhibit extended binary stacks in the solid state.

Cover Picture: Trimeric Perfluoro‐ortho‐phenylenemercury: A Versatile Lewis Acidic Host (Chem. Eur. J. 21/2003)

AbstractThe cover picture shows how trimeric perfluoro‐ortho‐phenylene mercury (center), one of the simplest trifunctional Lewis acidic hosts, interacts with organic molecules to afford various adducts. The planarity of this trinuclear complex as well as its overall polarizability compounded with relativistic effects at mercury permits the occurrence of noncovalent interactions and accounts for the tendency of this compound to form cofacial dimers as observed in the structure of the acetone adduct (top left). With a triply coordinated acetone molecule, the structure of this adduct also substantiates the cooperative effects that arise from the proximity and accessibility of the mercury centers. The complexation of arenes, such as benzene (bottom left) and naphthalene (bottom right), also occurs and leads to the formation of binary stacks in which the arene establishes multiple linkages with the mercury centers of the trifunctional Lewis acids. In addition to displaying unusual coordination environment, the arene units present in those stacks exhibit remarkable phosphorescent properties. For more details, see the paper by F. P. Gabbaï, R. E. Taylor, and M. R. Haneline on p. 5188 ff.

Methyl substituted benzene adducts of trimeric perfluoro-o-phenylene mercury

Trimeric perfluoro-ortho-phenylene mercury (1) dissolves in substituted benzenes including toluene, ortho-xylene, meta-xylene, para-xylene and is sparingly soluble in mesitylene. The 199Hg NMR resonance of 1 in toluene, ortho-xylene, meta-xylene, and para-xylene appears at δ −1051.8, −1053.5, −1051.4 and −1059.1 ppm, respectively. These resonances are slightly upfield from the resonance observed for 1 in CH2Cl2 (δ −1045.2 ppm) and possibly indicates the solvation of the mercury centres by molecules of arenes. Slow evaporation of solutions of 1 in toluene, ortho-xylene, meta-xylene, para-xylene and mesitylene affords 1·toluene (2), 1·ortho-xylene (3), 1·meta-xylene (4), 1·para-xylene (5) and 1·mesitylene (6), respectively, as crystalline complexes. These adducts have been characterized by elemental analysis and X-ray crystallography. Thermogravimetric analyses indicate that 2–5 begin to lose the coordinated arene at a temperature below 50 °C; however, in the case of 6 loss begins around 91 °C. The structures of 2, 4 and 5 reveals the existence of binary stacks in which the aromatic core of the benzenes approaches the mercury centres of 1. In the case of 3 and 6, the aromatic molecule appears preferentially bound to one of the two proximal molecules of 1. Hence, 3 and 6 are best described as discrete 1 ∶ 1 complexes. In 2–6, the resulting Hg⋯Caromatic distances are in the range 3.2–3.5 A and are within the sum of the van der Waals radii. They reflect the presence of secondary polyhapto π-interactions occurring between the electron-rich aromatic molecules and the acidic mercury centres.

Pi-complexation of biphenyl, naphthalene, and triphenylene to trimeric perfluoro-ortho-phenylene mercury. Formation of extended binary stacks with unusual luminescent properties.

Trimeric perfluoro-ortho-phenylene mercury (1) crystallizes from CS(2) as a pure compound. In the crystal, 1 forms staggered cofacial dimers (centroid distance of 3.38 A). In the dimer, the individual components are associated via long mercury-pi interactions (3.443 < Hg...C < 3.650 A). Interestingly, this arrangement leads to the existence of relatively short intermolecular mercury-mercury distances (3.811 < Hg...Hg < 4.093 A). In this form, compound 1 is photoluminescent and exhibits a broad emission band with a maximum at 440 nm and a shoulder at 530 nm. Compound 1 interacts with biphenyl, naphthalene, or triphenylene to form 1.biphenyl (2), 1.naphthalene (3), and 1.triphenylene (4), respectively. These adducts have been characterized by elemental analysis and X-ray crystallography. Their structure reveals the existence of stacks in which molecules of 1 and molecules of arenes alternate. In each stack, secondary pi-interactions occur between the arene and the mercury centers of 1. The resulting Hg...C distances range from 3.25 to 3.55 A and are within the sum of the van der Waals radii. They reflect the presence of secondary polyhapto-pi interactions occurring between the electron-rich aromatic molecules and the acidic mercury centers. In the case of the triphenylene adduct 4, a arene-fluoroarene interaction is also observed (centroid distance of 3.605 A). Compounds 2-4 are photoluminescent. The emission observed for 2 and 3 corresponds to the phosphorescence of the aromatic substrate and suggests the occurrence of a mercury heavy atom effect. In the case of 4, the emission appears at longer wavelengths than those typically observed for triphenylene.

Layered Perovskite-Like Crystals with (A1+C1) Stacks in the Structure

Crystal-chemical analysis has been performed on layered perovskite-like structures with (A1+C1) binary stacks, which are combinations of anionic octahedra with halves of degenerate octahedra (semioctahedra). Crystal data are reported for 56 possible prephases, of which 54 are new ones. Recommendations for syntheses of new compounds are given.

Influence of decreasing solvent polarity (dioxane–water mixtures) on the stability and structure of binary and ternary complexes of adenosine 5′-triphosphate and uridine 5′-triphosphate

The influence of dioxane on the complex equilibria involving the reactants adenosine 5′-triphosphate (ATP4–), uridine 5′-triphosphate (UTP4–), Cu2+, 2,2′-bipyridyl (bipy), and 1,10-phenanthroline (phen) has been determined. The concentration dependence of the chemical shifts of the protons of bipy and phen has been measured and the self-association property of these aromatic ligands (arm) was quantified with the isodesmic model of indefinite non-co-operative stacking. The stacking tendency is considerably diminished by dioxane: e.g., in D2O Kphenself= 31.1 ± 3.4 l mol–1 and in 50%(v/v)[2H8]dioxane–D2O kphenself= 0.63 ± 0.13 l mol–1. Similarly, the formation of the binary stacks (arm)(ATP)4– is also inhibited by dioxane: the stability of these adducts decreases by factors of Ca. 1/20 (or more) by changing the solvent from water to 50%(v/v) dioxane–water. The acidity constants of the mentioned (two-fold protonated) nucleoside 5′-triphosphates (NTP) and the stability constants of their binary and ternary complexes have been determined by potentiometric pH titrations in water, 30 and 50%(v/v) dioxane–water. By using the results obtained for the UTP systems mainly for comparisons, the following three intramolecular equilibria have been evaluated. (i) The proton in Cu(H-ATP)–may be located at N-1 or at the terminal γ-phosphate group: in water the isomer with the proton at N-1 occurs in significant amounts (∼50%), while in the dioxane–water mixtures the phosphate-protonated isomer strongly dominates. (ii) Cu(ATP)2– exists in two forms: one isomer has a phosphate co-ordination only, while the other is a macrochelate involving in addition N-7; the macrochelated isomer decreases from 68% in water to about 24% in 50% dioxane–water. (iii) While there is evidence that intramolecular stacks may also be formed in Cu(arm)(H-NTP)– and Cu(arm)(UTP)2–(and as far as possible their formation was quantified), the extent of stacking in the Cu(arm)(ATP)2– systems could be well characterized: e.g., with Cu(phen)(ATP)2– in water, ca. 92% exists in the stacked form and in 50%(v/v) dioxane–water ca. 49% of the ternary complex still remains stacked. This means, by going from water to 50% dioxane–water the stability of the metal-bridged Cu(arm)(NTP)2– stacks decreases only by a factor of Ca. 1/2, while the stability of unbridged binary (arm)(NTP)4– stacks decreases by Ca. 1/20 (or more). Similar trends are expected for the corresponding equilibria with other metal ions; the related search for selectivity regarding biological systems is discussed.